Miniature piezoelectric hollow sphere transducers

Miniature piezoelectric transducers were prepared from millimeter size hollow spheres which have been formed from PZT-SA powder slurries with a coaxial nozzle process. After sintering, the spheres were poled in two ways: radially and tangentially. Principal modes of vibration were found to be a breathing mode near 700 kHz and a thickness mode near 13 MHz for the radially poled spheres, and an ellipsoidal, a circumferential and a breathing mode near 230 kHz, 350 kHz, 700 kHz, respectively for tangentially poled spheres. Coupled modes were also observed at higher frequencies. These same modes with similar frequencies were obtained from finite element analysis using the ATILA FEM code, and experimental results were shown to be consistent with the modeling study. Hydrostatic dh coefficients were found to vary between 700-1,800 pC/N which are orders of magnitude higher than the d(h) of bulk PZT. The hydrophone figure of merits (d(h)*g(h)) were calculated to be between 68,000-325,000*10(-15) m(2)/N for various types of poled spheres. These values are three orders of magnitude higher than the bulk PZT figure of merit. Potential applications include ultrasonic imaging, non-destructive testing and hydrophones.